1. Field of the Invention
The invention relates to a motor operator for opening or closing contacts of switchgear adapted for use in mains power distribution systems such as public power distribution. The motor of the operator may be activated either locally or remotely to open or close the contacts of the switchgear. Alternatively, a drive element, normally coupling the motor to the contact operating shaft, is selectively removable so that a wrench-like handle may be used to manually open and close the contacts in case of failure of the motor operator or as a safety precaution.
2. Description of the Prior Art
Underground or pole mounted electrical transmission and distribution systems include a main service line leading from a sub-station with a number of individual distribution lines along the main line connected thereto. It is often the practice, particularly where power is supplied to a user entity such as a discrete residential area, industrial area or shopping area, to provide switchgear in each of the lateral distribution lines connected to the main line in order to allow selective de-energization of the lateral distribution line without the necessity of de-energizing all of the lateral distribution lines. Switchgear conventionally includes electrical, movable contacts which may be opened and closed by maintenance personnel in case of fault in or maintenance of a distribution line. In a particularly useful type of switchgear, the contacts are mounted under oil or in an inert gas atmosphere.
Generally, the contacts of switchgear require snap action opening and closing mechanisms to minimize arcing and assure a positive closing of the contacts. Actuation of the switch operating mechanism has normally been accomplished manually, requiring service personal to locate and travel to the switchgear in question. Recently, there has been increased interest in switch contact actuating mechanisms which are motor operated and can be activated at remote locations as well as manually locally. In some cases, motor operators have been installed within the switchgear cabinet itself for powered actuation of the opening and closing mechanism. By design, these motor operators are not suitable for installation on a retrofit basis on an external side of an existing switchgear cabinet. Moreover, most of the available motor gear operators are relatively expensive, both in terms of cost for various components, as well as expenses for installation of the same. Furthermore, these motor operators do not readily lend themselves to manual actuation in the event of motor failure or in the event that the operator desires to open the switch contacts by hand.
As a consequence of the fact that it is almost impossible to incorporate a motor operator in a switchgear cabinet, there is an increased interest in motor operators that could be mounted externally to the cabinet of the switchgear. In this respect it should be noted that it is not allowed to make any holes in the cabinet or make any weldings, which renders the mounting very difficult. It should also be considered that in most cases the motor operator should not only be weather proof but also secured against unauthorized intrusion. Further, it should be fully operable under all weather conditions and operate in a reliable manner.
An example of a motor operator to be mounted externally on a switch gear is dealt with in U.S. Pat. No. 4,804,809, saidwhich motor operator may even be mounted as a retrofit unit. The motor operator is composed of an assembly of individual elements mounted in a housing, necessitating a tedious dismounting of the connection between the motor operator and the switchgear for manually operating the switchgear.
Further, the motor operator has to be designed for each individual type of switchgear. This renders the motor operator costly.
For connection of the connection shaft of the motor operator to the operation shaft of the switchgear, the connection shaft has a first coupling part to fit with the coupling part of the switchgear in a longitudinal axial sliding and mutually rotational interlocking manner. A problem is that the coupling part of the switchgear differs depending on the various manufactures of switchgear and hence requiring a dedicated construction of the motor operator. In U.S. Pat. No. 4,804,809 the coupling part of the connection shaft is formed of an end of the shaft with a hexagonal cross section. Although not shown, the coupling part of the operation shaft is obviously a socket with a corresponding cross section. Similar in U.S. Pat. No. 5,895,987 the coupling part of the switchgear is an end of the operation shaft, but with a pentagonal cross section and with a key groove in one surface. The coupling part of the connection shaft is likewise a socket with a corresponding cross section. Other geometrical shapes used are square and a rhombus. In U.S. Pat. No. 5,025,171 it is the other way round; the coupling part of the operation shaft being an end of the shaft and the coupling part of the connection shaft being a socket, however, the specific geometry is not given.
Hence, there is a need for a motor operator which overcomes these and other problems associated with known devices.
It is an object of the present invention to provide a motor operator which is easy to mount and can be mounted on switchgear from various manufacturers of switchgear.
According to the invention this is accomplished in that the coupling part of the connection shaft is a separate interchangeable part of the connection shaft attached thereto by non-rotational interlocking means. Thus, it is possible to use one motor operator for switchgear of various brands, simply by choosing the relevant coupling part. It is of no consequence that the motor operator is of the type, which also could be operated manually as the operating tool, such as a handle, is the same irrespective of the switchgear brand. Accordingly, this provides a magnificent freedom in the overall design of the motor operator as it is no longer dedicated to a special switchgear brand. A further advantage is that the motor operator is more maintenance friendly. In case of a fault it could swiftly be replaced with a new one.
It is understood that the interconnection between the coupling part and the connection shaft could be realized in various manners. Overall it should lock to the connection shaft to participate in the rotation of this.
A dog-socket connection is preferred, where the coupling part of the connection shaft could be slid axially on the coupling part of the switchgear. However, the socket could have an opening in the side for laterally receiving the dog. It is understood that the coupling part of the switch gear could be a dog and the coupling part of the connection shaft a socket or vise versa.
In an embodiment the connection is a spline connection, especially with fine mating longitudinal V-shaped ribs distributed around the mating surfaces of the spline connection with an angle of 6° or about 6°. This safeguards that a connection with the switchgear easily could be established in a manner such that the motor operator takes an upright position or any other desired position.
In a preferred embodiment of the invention, a release mechanism is build into the actuator decoupling the activation element from the motor and transmission, thereby allowing the activation element to be moved manually. Accordingly, when activating the release mechanism, it is without further notice possible to operate the switchgear manually, e.g., by means of a wrench. The release mechanism also possesses the inherit characteristic that even in case the motor unintentionally is operated, it is still unable to operate the switchgear. This release mechanism could also be deployed to test the drive mechanism of the actuator to see if it works properly.
According to an embodiment the activation knob of the motor operator is identical to the coupling part on the switchgear such that the dedicated tool for the coupling part could be used for manually operating of the switchgear through the motor operater.
Accordingly, it would be understood that the overall size of the motor operator could be relatively compact and may be readily mounted also as a retrofit unit on the external side of an existing switchgear cabinet.